Project Summary/Abstract Crohn's disease (CD), a serious chronic inflammatory bowel disease (IBD) that was once considered rare in the pediatric population, is recently recognized as one of the most important chronic diseases that affect children and adolescents, with increasing incidence in youths of varying ages. As childhood is a time of physical, emotional, and social maturation, onset of CD in childhood can seriously delay growth, jeopardize mental health, and the negative impact may last a lifetime. In current pediatric CD research, disease activity is commonly evaluated at pre- specified time points post treatment for comparison of treatments and prediction of long-term outcomes. Findings from these studies are based on snapshots of patients' responses, with limited information on the temporal nature of disease progression. In addition, discrete analyses of disease activity fail to provide insights on functional relationship between treatment and growth, which is essential for selection of treatment to induce and maintain remission while optimizing the patient's growth and well-being. To fill this vital gap, we propose to 1) develop a series of statistical tools to characterize and identify patterns of disease trajectory of pediatric CD (PCD), and 2) incorporate the temporal information contained in disease trajectory for evaluation of treatments and prediction of long- term outcomes. The deliverables of this project will contribute to comprehensive understanding of PCD etiology, improvement of evidence-based treatment strategy for PCD patients, and may lead to changes toward better clinical practice regarding the criteria for optimized care for PCD patients. We will harness the large pediatric population from PEDSnet, a national pediatric learning health system, to empower the research findings and impacts. The data come from eight of the nation's largest pediatric health systems (including the Boston Children's Hospital, Children's hospital of Philadelphia and Cincinnati Children's Hospital Medical Center), covering more than 6 million children in total and 15 thousand with IBD diagnosis from 2009 to 2017. Furthermore, new knowledge and open-source software generated from our research will be integrated in real time with healthcare delivery systems to improve health care. Successful development of this proposed research has a promise of direct impacting the PCD patients in the PEDSnet and nationwide.